System and method for isotope ratio analysis and gas detection by photoacoustics

Abstract

A system and method are set forth for photoacoustical analysis of isotope and other compounds having telltale absorption wavelengths between 1700-2500 nm. The system and method includes a Co:Mg F 2 , optical parametric oscillator (OPO) or diode laser tunable between 1700-2500 nm which is directed into a sample at energies sufficient to generate detectable acoustical emissions. A microphone detects the emissions for processing and analysis. The system and method is adapted to detect stable isotope compounds such as 13 CO 2 as well as other chemical compounds. For non-gaseous compounds, a CO 2 or diode laser is used to photoablate the baseous sample containing the suspected compounds.

What is claimed is: 
     
       1. A method for examining a metabolic condition of an organism comprising: introducing a stable isotope compound into the organism for uptake by the metabolic system, the compound being metabolized and removed from the organism as a sample, said sample containing the isotope in a form having an absorption wavelength between 1700 and 2500 nm; directing the removed sample to a gas chromatograph to isolate various components of the sample;   directing the isolated components of the sample to a combustor to convert the effluents from the gas chromatograph to a CO 2  form of the sample;   directing the pulsed output of a laser into the CO 2  form of the sample, said laser being tuned through the wavelengths corresponding to the absorption wavelengths of the compound containing the metabolized isotope and having sufficient energy to generate acoustical waves in response to the presence of the isotope compound;   detecting the acoustic waves and generating an electrical signal proportional to the acoustical emission; and   processing the electrical signal to extract constituent gas acoustic emissions from background acoustical emissions over a plurality of pulses to improve the signal to noise ratio.     
     
     
       2. The method of claim 1 including directing the pulsed output of a Co:MgF 2  laser into the sample, said laser tunable between 1700-2500 nm and having an output at energy levels of 1-160 mJ. 
     
     
       3. The method of claim 1 including directing the pulsed output of an optical parametric oscillator laser into the sample, said laser tunable between 1700-2500 nm and having an output at energy levels of 1-160 mJ. 
     
     
       4. The method of claim 1 including directing the pulsed output of a diode laser into the sample, said laser tunable between 1700-2500 nm and having an output at energy levels of 1-160 mJ. 
     
     
       5. The method of claim 1 including introducing a  13  C labeled fat compound, the organism metabolizing the fat, the  13  C isotope removed from the organism as a  13  CO 2  exhalation sample. 
     
     
       6. The method of claim 1 including introducing a  13  C labeled bile acid and galactose compound, the organism metabolizing the compound, the  13  C isotope removed from the organism as a  13  CO 2  exhalation sample.